THE NEW WORLD MONKEYS 39
It is sometimes very beautifully coloured. The tail may be completely furry, or there may be naked areas of skin with papillary ridges. The hairs form a mane in the Lion Marmoset and a beard in the Howling Monkeys. They are implanted in groups of three, four or five.
No ischial callosities are present. The peri-anal skin has marked odoriferous glands in the Marmosets.
The Skull.—When the skull of any Platyrrhine Monkey is compared with that of a Mascarene Lemur two striking differences are at once seen—the cranial part is more expanded, and the facial skeleton is considerably reduced (fig. 11).
The skull varies in shape. In the Howling Monkeys the vertical depth is greater than the length; and the foramen magnum is situated on the flat back part. To a lesser extent this condition is present in CaUicebus, Aotus, Pithecia and Lagothru. In Ateles, Gelus and the Hapalidae the skull is elongated, with a muzzle; the occipital region is convex, and the foramen magnum is-on the basis cranii; so there is some resemblance to the human skull.
The orbits vary in size, and have their axes directed forwards and slightly outwards. They are shut off from the temporal fossa, only the spheno-rnaxillary fissure being left of the wide communication which exists in the Lemurs. The lachrymal orifice is within the orbit. The interorbital width varies.
The malar bones have marked foramina for the passage of a nerve. The anterior narial aperture is oval or triangular. It is bounded by the premaxillse and nasal bones.